Technical Abstract:
Many organic soybean producers face the challenge of bean leaf beetle (Ceratoma trifurcata), which harbors bean mottle pod virus and opens infection sites for Fusarium spp., Cercospora kikuchii, and Phomopsis spp., which cause discoloration in soybeans. Stained soybean seed is less acceptable for food-grade markets (e.g., tofu), but increasing demand for organic meat and a premium for organic feed-grade soybean has encouraged producers to continue growing the crop. From 2001-2006, organic soybean varieties were tested at the Neely-Kinyon Farm in southwest Iowa, using different biological treatments to manage bean leaf beetle populations. Plots with a 6-m cultivated border to deter insect movement between plots were laid out in a completely randomized design. Biological treatments included single or combination applications of baking soda, hydrogen peroxide, molasses, Neemix 4.5TM, SurroundTM, Garlic BarrierTM, HexacideTM, EntrustTM, and PyganicTM. Treatments were compared with a control. Each year, treatments were applied every 2 weeks, corresponding with the crop's growing cycle. Bean leaf beetle and other beneficial or pest insect sampling occurred on alternate weeks from June to September, by sweeping across plants in each plot and examining plants for insect populations. While the organic farmers who requested this study found some reduction in beetle populations and subsequent soybean staining on their farms with these treatments, our results did not find any significant differences between the treatments and the control. Organic soybean yields were excellent from 2001 to 2006, however, ranging from 2.5 to 4.0 Mg/ha, and were highest in 2005 and 2006. Plots using biological treatments Pyganic™, Entrust™, and Hexacide™ tended to have the greatest overall mean yields. We will continue to examine different treatments and will study the interaction between variety and soybean staining to assist farmers in making the best choice of organic soybean based on market demands.